In various industries, mixers are used to uniformly mix various particulate materials. In many industries, for example mining, power generation, and oil sands, tailings are mixed with water to produce a material of consistent water content—a conditioned tailings to be used for further processing. In the mining industry, tailings result from the refinement of ore. These tailings are sometimes mixed together with water and cement to provide fill for underground mining methods. These tailings particles usually cover a spectrum of particle sizes ranging from clay size particles to sand sized particles (typically <1 μm to >1 mm). When using the tailings to produce minefill, it is sometimes desirable to dewater the tailings to generate a fill with sufficient strength and pumpability at an optimized cost. Controlling the moisture content of the tailings is necessary to produce a fill with predictable strength. The process of producing tailings at a consistent moisture content is often accomplished by filtering part of the tailings stream and recombining it with a controlled amount of water to reach a target moisture content. Filtration of many tailings materials generates cohesive ‘lumps’ of material. In the case of minefill the lumps in the material can create problems with pumping the fill through pipelines. As such, these cohesive lumps are introduced into a mixer for mixing and conditioning with water to reduce the size and amount of lumps. Current mixers on the markets, however, are only designed for mixing and are inefficient at breaking down the lumps in the material.
Various types of mixers which are known to be used for mixing various paste-like mixtures include horizontal single and twin shaft mixers, ribbon mixers, pan mixers, and planetary mixers. In a horizontal shaft mixer, conventional mixing blades are typically provided with a leading surface at an angle to the direction of motion, generally around 30 degrees off the normal plane of the motion vector. This pushes material to slide off the paddle and urges the material within the mixer not only in the circumferential direction of motion of the paddle, but also out of the plane of the motion of the paddles in an axial direction of the shaft. These motions of the material are required to effectively mix the material inside the mixer.
The leading surface of the paddles are close to normal or even with a positive angle to the tangential surface (ie the boundary wall) of the mixer, and the leading edge of the paddle is adjusted to be directly adjacent to the boundary wall to prevent coarse gravel from being crushed between the paddle and the surface of the mixer. The leading edge is also close to the boundary wall of the mixer because that will scrape any material off the wall to ensure that the mixer stays clean without buildup along the surfaces of the boundary walls of the mixing chamber of the mixer.
Although the arrangement of the mixing paddles described above have been found to be effective for mixing the paste, the known arrangement of paddles are ineffective at breaking up lumps or reducing lump size when mixing a paste-like mixture of moistened fine particles which has a tendency to clump.